The present invention relates generally to sensor systems, and more particularly, to an improved sensor system including a door sensing edge having an infrared or photoelectric transmitter and receiver with a control circuit capable of reducing detection errors due to noise.
Conventional sensing edges generally include a sheath having a cavity formed along the length of the sheath wherein at least a portion of a switch is located. The sensing edge is attached to an edge of a door which may be moved in different directions. When external pressure is applied to the sheath of the sensing edge, the switch is activated. The activated switch actuates a door control device, which in turn causes the door to either stop moving or to open. For example, the external pressure may be applied to the sheath when the sheath contacts an obstructing article such as a tool or a portion of the body of a person, located between the sensing edge and an opposed surface. By stopping or changing the direction of movement of the door, damage to the obstructing article may be prevented.
Many types of conventional sensing edges that operate generally as described above are in existence today. For example, a first conventional sensing edge includes a photoelectric switch comprising a light transmitter and a light detector. The light transmitter and the light detector are positioned a predetermined distance below a leading edge of a door and at opposite ends of the leading edge such that the light transmitter transmits a light beam across the length of the door toward the light detector. The light beam is blocked from reaching the light detector when an article obstructs the downward movement of the door. When the light detector senses the absence of the light beam, the light detector sends a signal to a door control device, which in turn causes the door to either stop moving or to open.
The first conventional sensing edge is flawed because the light transmitter and light detector are not contained within a protective covering, such as a sheath. Therefore, the light transmitter and the light detector are subject to damage from natural forces (such as rain, wind, snow, etc.) and artificial forces (such as misdirected balls, errant bicycles, maliciously thrown rocks, etc.).
A second conventional sensing edge described in U.S. Pat. No. 5,426,293, which is incorporated by reference herein, includes a device for controlling movement of a door by actuation of the device upon an external force being applied to a sensing edge. The sensing edge includes an elongated, generally flexible tubular sheath which is secured to a leading edge of the door. The sheath includes an elongated hollow cavity with an optically reflective interior surface. A light transmitter is positioned proximate a first end of the sheath for transmitting a light beam toward a second end of the sheath. A light detector is positioned proximate the second end of the sheath for detecting the presence or absence of the light beam at the second sheath end. The light detector generates a signal for actuating the device upon detecting the absence of the light beam at the second end of the sheath.
The second conventional sensing edge is flawed because light detectors often detect noise and other short term transients, not due to actual obstructions in the path of the leading edge of the door. Such noise and other transients, which are detected instantly, causes the device to actuate the door erroneously.
What is required is a sensing edge having a photoelectric sensor system including a transmitter and a receiver (light wave or infrared), wherein the transmitter and the receiver have noise and transient immunity provided by a specially designed control circuit.
Briefly stated, the present invention comprises a sensor system for controlling movement of a door moving in a first direction by actuation of a device. The sensor system includes an elongated generally flexible tubular sheath secured to a leading edge of the door, the sheath having a longitudinal axis generally parallel to the leading edge of the door and including an elongated hollow cavity extending generally parallel to the longitudinal axis, a first open end, and a second open end. An infrared transmitter is located near the first end of the sheath for transmitting an infrared signal toward the second end of the sheath through the cavity. An alternate embodiment may include a light wave transmitter in lieu of the infrared transmitter. The sensor system also has an infrared receiver near the second end of the sheath in alignment with the infrared transmitter for detecting the infrared signal at the second end, and for generating an output signal upon detecting an absence of the infrared signal when the passage of the infrared signal through the cavity is blocked. If the transmitter is a light wave transmitter, then the receiver may be a light wave receiver in place of an infrared receiver. The sensor system may alternatively use any electromagnetic emitter as a transmitter and a corresponding electromagnetic detector as a receiver, such as radio wave, microwave, x-ray, and the like. The sensor system also has a control circuit coupled to the receiver for receiving the output signal from the receiver and for sending a failure signal to the device only if no signal is received by the receiver for a predetermined time period.